10-02: Determining the Impact of Cations and Anions of Ionic Liquids on Biomass Pretreatment Efficiency

Imidazolium based ionic liquids (ILs), specifically 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]), have been shown to be effective at pretreating biomass. The resulting pretreated materials can be readily hydrolyzed by commercial enzyme mixtures with high yields of fermentable monomeric sugars obtained over relatively short reaction times. Despite these advantages, IL cost, IL recycling, and generation of inhibitors hamper rapid commercialization of future biorefineries using an IL pretreatment platform.

Recently, cholinium cation amino acid anion ILs, a new type of bio-ILs, have been reported to pretreat biomass with great efficiency at temperatures lower than 100 ^oC. In order to understand the mechanism and the role of cations and anions on biomass pretreatment efficiency, we selected four ILs with different combinations of cations: 1-ethyl-3-methylimidazolium ([C₂mim]) vs. cholinium ([Ch]) and anions: acetate ([OAc]) vs. lysinate ([Lys]). The results indicate that ILs with [Lys] anion perform better than [OAc] anion in terms of delignification and sugar production at pretreatment temperatures lower than 100 ^oC. The Kamlet-Tamft parameters indicate that both [C₂mim][Lys] and [Ch][Lys] have much higher hydrogen bonding basicity (β value) than the ILs with [OAc] a characteristic we hypothesize is directly related to sugar yield.